1. Field of the Invention
The present invention relates to a speed control method for recording data on an optical disk, and more particularly, to a speed control method for recording data on a rewritable optical disk.
2. Description of the Prior Art
Generally speaking, in a recordable optical disk drive, there are several speed control methods of recording data on an optical disk (CD-R or CD-RW).
(1) Constant Linear Velocity, CLV:CLV means that the optical disk is controlled such that a track length passing by an optical pickup head per unit time is constant. That is to say, when the optical pickup head accesses the inner region of an optical disk, a spindle motor rotates faster. On the contrary, when the optical pickup head accesses the outer region of an optical disk, the spindle motor rotates slower. Under the control of CLV, the rotation speed of the spindle motor is related to the position of the pickup head relative to the optical disk. That is, when the optical pickup head is moving from the inner to the outer region of the optical disk, the rotation speed of the spindle motor is gradually slowing down. Generally, a 1× optical disk drive is defined as the relative velocity between the optical pickup head and the optical disk being from 1.2 m/s to 1.4 m/s with 4.3218 MB/s data transmission rate. Other optical disk drives with higher speeds are defined as integer multiples of the above values, such as 2×, 4×, 8×, 16×, 20×, etc.
The advantages of CLV are as follows. (1) The data transmission rate is steady so that data can be written onto the optical disk with the steady laser beam power for ensuring writing quality. (2) The average data transmission rate is high. However, the disadvantages of CLV are as follows. (1) The service life of the spindle motor is short due to the variable rotation speed according to the position of pickup head relative to the optical disk. (2) If the data transmission rate is too high, the rotation speed of the spindle motor cannot keep up with the transmission rate especially at the inner region of the optical disk.
(2) Constant Angular Velocity, CAV:CAV means that the rotation speed of the spindle motor is constant. When the rotation speed of the spindle motor is constant, the data transmission rates at the inner and the outer regions of the optical disk differ substantially. In other words, when the optical pickup head accesses the inner region of the optical disk, the data transmission rate is lower; on the contrary, when the optical pickup head accesses the outer region of the optical disk, the data transmission rate is higher.
The advantages of CAV are as follows. (1) The service life of the spindle motor is long due to the constant rotation speed of the spindle motor. (2) The data transmission rate of CAV is higher than the data transmission rate of CLV in the random access case because the rotation speed of the spindle motor of CAV is constant and the rotation speed of the spindle motor of CLV is variable. The drawbacks of CAV are as follows. (1) The laser power is altered according to the variable data transmission rate, thus the writing quality is not easily controlled. (2) The average data transmission rate is low.
(3) Zoned Constant Linear Velocity, ZCLV:ZCLV means that the optical disk is divided into several regions from the inner to the outer region and the transmission rate of individual region is constant as in CLV. ZCLV is a combination of CLV and linking technology. Please refer to FIG. 1. FIG. 1 is a diagram of data transmission rate versus position of an optical disk when performing data writing under ZCLV in the prior art (the unit defining the position of the optical disk is time). In this case, the optical disk is divided into three zones. Before the time point T1 (region 1), the data transmission rate is 16× for performing data writing. Between the time points T1 and T2 (region 2), the data transmission rate is 20× for performing data writing. And after the time T2 (region 3), the data transmission rate is 24× for performing data writing. When changing from a region to another region, super-link technology is used to connect the two regions with different data transmission rates. That is, the writing process can be interrupted and be restarted with the super-link technology. Therefore, there are zone link situations at the time points T1 and T2.
ZCLV improves the drawback of CLV that if the data transmission rate is too great, the rotation speed of the spindle motor cannot keep up with the transmission rate, and keeps an advantage of CLV, which is that the transmission rate is steady. However, ZCLV still cannot improve the short service life of the spindle motor, one of the drawbacks of CLV, and ZCLV has lower average transmission rate compared with the average transmission rate of CLV.
(4) Partial Constant Angular Velocity, PCAV:PCLV means that the data transmission rate is increasing as the movement of the pickup head from inner region to outer region of the optical disc until the data transmission rate reaches the highest data transmission rate that the disc allowed or the highest data transmission rate that the optical disc drive provides, and the data transmission rate will be maintained at a constant value that equals to the highest speed. Please refer to FIG. 2. FIG. 2 is a diagram of data transmission rate versus position of an optical disk when performing data writing under PCAV in the prior art (the unit defining the position of the optical disk is time). In this case, the optical disk is divided into a CLV region and a CAV region with the time point T4 of the optical disk. Before the time point T4, the spindle motor provides a constant rotation speed; therefore, the initial data transmission rate is 4×. And the data transmission rate increases to 10× when the optical pickup head reaches the T4 position of the optical disk. After the time point T4, the data transmission rate stays at 10× CLV for performing data writing.
PCLV keeps advantages of CAV and overcomes an disadvantage of CAV, namely that the low average transmission rate. In addition, performing data writing under PCAV can increase the rotation speed of the spindle motor and prevent zone-link due to switching the data transmission rate under ZCLV.
Recording speed of a rewritable optical disk is often limited within a range, such as from 1× to 4× or from 12× to 24×, due to disk process. When performing data writing under CAV, the ratio of the data transmission rate at the inner region to the data transmission rate at the outer region is 1:2.4. In other words, as to a rewritable optical disk with a maximum data transmission rate 24×, the data transmission rate in the inner region is 10×. However if the allowable minimum data transmission rate of the rewritable optical disk is 12×, the data writing quality will be reduced within the data transmission rate range of 10× to 12×. Thus, performing data writing on some rewritable optical disks under CAV reduces the data writing quality.